Cardiovascular (CV) diseases are a leading cause of morbidity, mortality, and burden on healthcare around the world, with about 7 million cases of heart failure and many more cases of myocardial infarction in the United States alone. Acute and chronic CV conditions reduce quality of life and life expectancy. A variety of treatment modalities have been developed for CV disease, ranging from pharmaceuticals to mechanical devices and finally transplantation. Temporary cardiac support devices, such as ventricular assist devices, provide hemodynamic support, and facilitate heart recovery.
There are many types of temporary cardiac assist devices with varying degrees of support and invasiveness, from intra-aortic balloon pumps (IABP) to extracorporeal membrane oxygenation (ECMO) devices to left ventricular assist devices (LVAD) implanted surgically. These devices commonly reside outside the ventricle or bypass the ventricle, and do not work in parallel with or directly support heart function. They also do not provide clinicians with quantifiable metrics that can guide the level of cardiac support that is required for a particular patient. Some ventricular assist devices are percutaneously inserted into the heart and can run in parallel with the native heart to supplement cardiac output, such as the IMPELLA® family of devices (Abiomed, Inc., Danvers Mass.).
The amount of support (e.g., volumetric flow rate of blood delivered by the pumping device) and/or the duration of support each patient needs can vary. It has been suggested that variations in the motor current required to maintain a rotor speed can be utilized to understand placement of the pump or pump function, but these proposals have fallen short of usefully processing the motor current data to measure cardiac function. For example, U.S. Pat. No. 6,176,822 describes measuring motor current to aid in proper positioning of the pump, and U.S. Pat. No. 7,022,100 mentions calculating blood pressure based on the relationship between the torque and motor current of a motor used to drive the rotor. However, the motor current alone provides only limited insights into a patient's overall cardiac function, and existing measures such as aortic pressure do not correlate to a patient's overall cardiac function. Accordingly, there is a need to more directly and quantitatively estimate metrics of cardiac function to aid clinicians in determining how much support a device should deliver or when to terminate use of a cardiac assist device.